Samples has changed to path tracing tile
Square Samples 

You have Square Samples feature turned on, which squares specified amount of samples. 
This means that if you set 150, it will calculate 22 500 samples (not the task you should try imho). 

In case of using Square Samples you'll see exact amount of them to be computed in the bottom of Samples scroll (it will be shown there only if Squares Samples turned on):



In your case, you have 12 samples specified in Render samples quantity, thus it'll render 144 samples.

Tiles or What is shown in the top of the rendered image

When rendering, in the top of the UV/Image Editor screen you have shown:


elapsed and remaining time, 
memory usage, 
current scene and Render Layer which is rendered, 
and amount of tiles - already rendered / remained to render.


Tiles are those small boxes which appear on the rendered image where calcualting is being done at the moment. They are the amount of work which Blender is able to calculate at once taking into account saved user preferences, scene specifics, and hardware.



So taking this situation, it calculated 570 small orange boxes of 2125. Tiles' quantity will change in several cases:


changing output resolution;
changing Auto Tile Size in Performance scroll


You can read more about tiles quantity vs. performance here. Generally, most likely you won't have to change Auto Tile Size setting, which is turned on by default.